A wide variety of automated chemical analyzers are known in the art and are continually being improved to increase analytical menu and throughput, to reduce turnaround time, and to decrease requisite sample volumes. These clinical analyzers may conduct assays using reagents to identify analytes in a biological fluid sample such as urine, blood serum, plasma, cerebrospinal liquids, and the like. For convenience and safety reasons, these fluid samples are almost universally contained within capped sample containers (e.g., sample tubes). The assay reactions generate various signals that may be manipulated to determine a concentration of analyte in the sample. See, for example, U.S. Pat. Nos. 7,101,715 and 5,985,672 assigned to the assignee of the present application and incorporated herein by reference. Improvements in clinical analyzer technology have been accompanied by corresponding advances in pre-analytical sample preparation and handling operations such as sorting, batch preparation, centrifugation of sample tubes to separate sample constituents, cap removal to facilitate fluid access, and the like by automated pre-analytical sample preparation systems called Laboratory Automation Systems (LASs). LASs automatically transport sample in sample tubes to a number of pre-analytical sample processing stations that have been “linked together” like described in U.S. Pat. Nos. 6,984,527 and 6,442,440, both incorporated herein by reference.
These LASs may handle a number of different patient specimens contained in standard, bar code-labeled, and evacuated sample tubes. The bar code label may contain an accession number that may be coupled and correlated to demographic information that may be entered into a hospital's Laboratory Information System (LIS) along with test orders and other desired information. An operator may place the labeled sample containers (e.g., tubes) onto the LAS system, which may automatically sort and route the sample tubes to the requisite processing devices for pre-analytical operations such as centrifugation, decapping, and aliquot preparation prior to the specimen being subjected to clinical analysis by one or more analytical stations that may also be “linked” to the LAS.
For certain clinical assays, a serum or plasma portion (obtained from whole blood by centrifugation) may be used in the clinical analysis. To prevent clotting, an anticoagulant such as citrate or heparin may be added to the blood specimen immediately after it is originally obtained. Alternatively, the anticoagulant may be placed in an empty sample container (e.g., tube) prior to the patient sample being obtained. At a later time, the specimen may be centrifuged to separate the serum or plasma portion from the red blood cell portion. A serum separator may be added to the sample container to aid in the separation of the red blood cell portion from the serum or plasma portion.
After centrifuging and a subsequent de-capping process, the open sample container (e.g., tube) may be transported to an appropriate clinical analyzer that may extract liquid specimen from the sample container and combine the specimen with one or more reagents in special reaction containers (e.g., cuvettes or cups). Analytical measurements may then be performed, often using a beam of interrogating radiation interacting with the sample-reagent combination, for example, by using photometric or fluorometric absorption readings or the like. The measurements allow determination of end-point or rate values from which an amount of analyte related to the health of the patient may be determined using well-known calibration techniques. Unfortunately, the presence of certain components (e.g., colored interferents) in the sample as a result of some preexisting sample condition or processing may adversely affect the accuracy of the results of the analyte measurement obtained from the clinical analyzer.
In some cases, the integrity of the serum or plasma portion of the specimen may affect the interpretation of the results, i.e., the analyte reading of the clinical analyzer. For example, pre-analytical variables in the serum or plasma portion, which are not related to the patient disease state, may cause a different interpretation of the disease condition of the patient. Pre-analytical variables include hemolysis (ruptured red blood cells), icterus (excessive bilirubin), and lipemia (high, visible lipid content).
Typically, the integrity of the serum or plasma portion of the specimen is visually inspected by a skilled laboratory technician. This may involve a review of the color of the serum or plasma portion of the specimen. A normal serum or plasma portion has a light yellow to light amber color. Alternately, a serum or plasma portion containing hemolysis may be quite reddish in color. Interferents may arise, for example, if an excess number of red blood cells are damaged, possibly during venipuncture, centrifugation, or after prolonged storage. When red blood cells are injured, they release low density, reddish-colored hemoglobin into the specimen causing a reddish-colored sample that is said to exhibit “hemolysis.” The presence of free hemoglobin (Hb) may be used to measure the degree of hemolysis and, when the hemoglobin concentration exceeds about 20 mg/dl, the hemoglobin may interfere with the colorimetric determination of analytes in the clinical analyzer due to the reddish interferent contained in the specimen.
A sample containing icterus may be dark yellow/brown in color. Such interferents may arise, for example, from an excess of bilirubin, the result of decaying red blood cells being converted in the spleen into bilirubin. Levels of bilirubin above 2-3 mg/dl are visibly yellowish and may, in particular, adversely affect enzyme-based immunoassays. Such a condition is termed bilirubinaemia or icterus.
A sample containing lipemia may be whitish in color. Interferents may arise, for example, as a whitish appearance in serum or plasma portion due to the presence of excess lipids. Such a condition is called lipemia and lipid levels above about 50 mg/dl may interfere with antibody binding in immunoassays and may accordingly also affect immunoassay results.
Thus, the degree of red color in a serum sample may correspond to the amount of hemolysis present in the serum or plasma portion of the specimen, the degree of dark yellow/brown color may correspond to the amount of icterus present in the serum or plasma portion of the specimen, and the degree of whitish color may correspond to the amount of lipemia present in the serum or plasma portion of the specimen.
Subsequent to centrifugation, when the red blood cell portion has been separated from the serum or plasma portion, a skilled technician may visually inspect the serum or plasma portion and, if judged to not have a normal light yellow to light amber color, the specimen may be discarded. Otherwise, the specimen will be processed and analyzed as ordered. However, visual inspection is very subjective, labor intensive, and fraught with the possibility of human error. Thus, various methods have been implemented to ascertain whether hemolysis, icterus, and lipemia (these three conditions are frequently called “HIL”) are present in a serum or plasma portion of the specimen.
Typically, a laboratory technician will assign a hemolytic index, an icteric index, and a lipemic index to the serum and plasma portion of the specimen based upon the color. Based upon the value of the hemolytic index, the icteric index, and the lipemic index, the interpretation of the results from the clinical analyzer can be evaluated. Alternately, if the value of one or more of the hemolytic index, the icteric index, and the lipemic index are too high, the specimen may be discarded without analysis by the clinical analyzer.
As mentioned above, visual inspection can be labor intensive and costly. Furthermore, the possibility of human error exists with visual inspection, the results of the visual inspection may be highly subjective and may vary between workers, and one variable could mask or hide other variables. Furthermore, with closed container sampling, bar code labels directly on the container, and the use of automated clinical analyzers, the laboratory technician, in many instances, may simply not have a clear opportunity to visually observe the serum or plasma portion of the specimen. Thus, it is becoming increasingly important to evaluate the integrity of the serum or plasma portion of the specimen without the use of visual inspection by a laboratory technician.
One attempt to solve this problem involves optically viewing the serum or plasma portion of the specimen after the serum or plasma portion has been transferred to one of the cuvettes of the clinical analyzer. Measuring the optical characteristics of the specimen in the clinical analyzer eliminates the need for visual inspection. However, this test utilizes machine time of the clinical analyzer and, if the integrity of the specimen is determined to be compromised, additional machine time and a machine cycle are wasted. Furthermore, this procedure cannot be used with clinical analyzers that add reagents to the cuvette prior to adding the serum or plasma portion of the specimen.
U.S. Pat. No. 5,734,468 discloses monitoring a serum sample with a detector that performs a spectrophotometric analysis of the serum sample in the probe lumen through a substantially transparent section of the probe. From the spectrophotometric analysis, a hemolytic index, an icteric index, and a lipemic index of the serum sample can be established. Based upon these serum indices, the serum sample can be transferred to a clinical analyzer for additional tests or can be disposed of because the sample is compromised.
U.S. Pat. No. 6,372,503 discloses quality control material used to monitor instrument calibrations or used for recalibration for instruments that assess the amount of hemolysis, turbidity, bilirubinemia, and biliverdinemia, either separately, or any two, or any three, or all four simultaneously, in plasma or serum samples.
U.S. Pat. No. 6,628,395 discloses preliminarily testing a sample for HIL in the original incoming sample container, prior to being removed from the container and prior to being transferred to a clinical analyzer. In this approach, sample is not consumed and can be transferred to the clinical analyzer or a waste receptacle based upon results of the evaluation.
U.S. Pat. No. 6,353,471 discloses a method to reject a sample from further analysis based on determining the concentration of at least one interferent in the sample by: (1) irradiating the sample with at least one frequency of radiation; (2) correlating absorbance of the radiation by the sample with a standard for the interferent(s) to determine the concentration of the interferent(s), and (3) rejecting the sample if the concentration of the interferent(s) exceeds a predetermined criteria.
One challenge in performing spectrophotometric analysis has been that the specimens are initially obtained in a variety of primary patient sample collection containers (“sample containers”). These sample containers are usually tubes of varying diameters and lengths. In the case of a patient blood sample, the liquid is often centrifuged to separate the liquid serum or plasma portion from the cellular phase (e.g., red blood cell portion). Such sample containers may have a patient identification label, varying and unpredictable amounts of the serum or plasma portion to be analyzed in the total specimen, and contain a relatively large amount of sample liquid.
Because of the problems encountered when endogenous interferents are contained within liquid samples to be clinically analyzed, there is an unmet need for a method and apparatus adapted to determine a presence of such interferents. The method and apparatus should not appreciably adversely affect the speed at which analytical test results are obtained and should allow making a determination on a relatively large sample portion so that the accuracy of such a determination is not affected. Furthermore, the method and apparatus should be able to be used even on labeled sample containers.